The present invention generally relates to control signals generating circuits for magnetic recording and/or reproducing apparatuses, and more particularly to a control signal generating circuit for an apparatus which magnetically records and/or reproduces a video signal. The control signal generating circuit according to the present invention generates a control signal by use of a vertical synchronizing signal which is separated from the video signal, and is designed so facilitate the manufacturing of the control signal generating circuit in the form of an integrated circuit.
Generally, an apparatus for magnetically recording and/or reproducing a video signal, comprises a control signal generating circuit. The control signal generating circuit generates a control signal during a recording mode, and this control signal is recorded on a control track of a magnetic tape. The control signal is used as a reference signal for controlling the rotation of rotary heads, for example. The control signal which is recorded on the magnetic tape, is reproduced during a reproducing mode and is used as a reference signal for controlling the rotation of a capstan, for example. In a case where the video signal is of the NTSC system, for example, this type of control signal generating circuit obtains a control signal having a frequency of 30 Hz, by separating a vertical synchronizing signal having a frequency of 60 Hz from the video signal and frequency-dividing the separated vertical synchronizing signal by 1/2.
As a conventional control signal generating circuit, there was a control signal generating circuit comprising the so-called CR monostable multivibrator circuit. This CR monostable multivibrator circuit included a capacitor and a resistor for determining a time constant for the purpose of frequency-dividing by 1/2 the vertical synchronizing signal which is separated from the video signal. However, when manufacturing this CR monostable multivibrator circuit in the form of an integrated circuit, the capacitor and the resistor had to be coupled externally of the integrated circuit, and there were disadvantages in that an integrated circuit should have many number of pins including a pin to be connected with the external capacitor and resister the control signal generating circuit as a whole could not be manufactured in the form of an integrated circuit. Further, there was another disadvantage in that the CR monostable multivibrator circuit included a large number of circuit elements.
As another example of a conventional control signal generating circuit, there was a control signal generating circuit comprising a digital pulse counting monostable multivibrator for frequency-dividing the separated vertical synchronizing signal by 1/2. The digital pulse counting monostable multivibrator included a crystal oscillator, and generated a control signal having a frequency of 30 Hz responsive to the vertical synchronizing signal supplied thereto by counting the pulses from the crystal oscillator. However, the cost of this other conventional control signal generating circuit became high, due to the provision of the expensive crystal oscillator. Further, approximately ten to twenty stages of counters were required to count the pulses from the crystal oscillator, and it was therefore impossible to manufacture the control signal generating circuit at a low cost.